Circular Nozzle Research Articles

Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.

Spray Characterization of Aerosol Delivery Systems for Use in Stored Product Facilities

HighlightsHandheld sprayers generated larger droplets and wider droplet size distributions than compressed gas sprayers.Sprayers with higher pressure and nozzles with wider spray angle produced smaller droplets.Droplet size distribution influenced spray coverage, mass concentration, deposition, and sprayer efficacy.The handheld sprayers had less spray coverage and efficiency than the compressed gas sprayers.The deposition at different locations was influenced by the volume of the space, aerosol dosage, and spray time.Abstract. Aerosol insecticides, including pyrethrins, can be used as methyl bromide replacements to control stored product insects inside flour mills and rice mills. The effectiveness of aerosol application for insect control requires knowing the spray characteristics of the equipment to be used and understanding factors that influence the effectiveness of insecticide application. The objectives of this study, as part of efforts to optimize aerosol applications, were to evaluate the characteristics of six aerosol delivery systems (two handheld sprayers and compressed gas sprayer systems fitted with two types of manifolds and two types of nozzles), estimate the dispersion and deposition of aerosol in a simulated stored product facility, and determine how the dispersion and deposition are affected by the characteristics of the sprayers. Results showed that the spray systems differed significantly in spray characteristics. The compressed gas sprayers generated significantly smaller droplets, more uniform droplet size distribution, and better spray coverage than the handheld sprayers. The ellipsoidal nozzle produced significantly smaller droplets than the circular nozzle. While the type of manifold had no significant effect on deposition, higher aerosol dosage and spray time resulted in significantly higher deposition. Results of this study will be used to improve spray techniques for stored product insect control, to validate computational fluid dynamics modeling of aerosol application, and to improve testing methods in large-scale spray testing inside commercial facilities. Keywords: APS spectrometer, Droplet size distribution, HELOS KR-Vario, Mass deposition, Spray characteristics, Spray nozzles.

Study of heat transfer characteristics from impinging jet with small diameter circular orifice nozzle at low Reynolds number

Study of heat transfer characteristics from impinging jet with small diameter circular orifice nozzle at low Reynolds number

Numerical analysis of enhanced mixing due to grooves in convergent – Divergent nozzle

The focus of this study is to improve the mixing at the exit of supersonic jet and estimate the decay of total pressure and Mach number by introducing interior grooves on top and bottom side alongside the divergent length of the convergent divergent nozzle. Geometrical model of the nozzle is created using CATIA software and analysis is performed using ANSYS. The decay of the total pressure and Mach number is studied for over expansion (4 bar), optimum expansion (6 bar) and under expansion (8 bar) instances by fixing Mach number at exit of the nozzle as 1.8 for nozzle configurations with and without inside grooves. The grooves act as passive controls ensuing significant enhancement of jet mixing. The decay of Mach number and total pressure alongside the jet centreline axis is greater for grooved nozzle in contrast to plain nozzle. The centreline axis total pressure decay comparison shows semi-circular grooved nozzle decays 30% faster than the plain circular nozzle, whereas square grooved nozzle decays 62% faster than the plain circular nozzle in under expansion condition. The characteristics of decay increased with increase in groove length.

Effects of Nozzle Geometries on 3D Printing of Clay Constructs: Quantifying Contour Deviation and Mechanical Properties

In this research, ready-to-print clay was employed to 3D print cylindrical constructs using two different nozzle geometries. The cylinders were printed using a direct ink writing (DIW) 3D printer with similar printing parameters such that the impacts of using different nozzle geometries in contour deviation and mechanical properties of the printed constructs can be quantified. Choosing the right nozzle geometry before printing is critical as it affects the surface finish as well as the mechanical properties of the constructs. This study utilizes point cloud data of the printed samples obtained from a scanning system to measure the contour deviation and surface roughness. According to the results from the point cloud analysis, for cylindrical constructs, circular nozzle imparts less surface roughness and contour deviation whereas square nozzle imparts higher compression strength but with comparatively higher contour deviation and surface roughness. The study provides framework to determine the deviations and mechanical properties of the free form constructs. The work has provided a guideline of nozzle selection in 3D printing of clay constructs for civil infrastructures.

Analysis of Gas-Solid Flow Characteristics in a Spouted Fluidized Bed Dryer by Means of Computational Particle Fluid Dynamics

In order to grasp the particle flow characteristics and energy consumption of industrial fluidized spouted beds, we conduct numerical simulations on the basis of a Computational Particle Fluid Dynamics (CPFD) approach. In particular, the traction model of Wen-Yu-Ergun is used and different inlet conditions are considered. Using a low-speed fluidizing gas, the flow state of the particles is better and the amount of particles accumulated at the bottom of the bed wall becomes smaller. For the same air intake, the energy loss of a circular nozzle is larger than that of a square nozzle.

Main geometrical features of horizontal buoyant jet fire and associated radiative fraction

AbstractHigh momentum release of jet fire can be very intense, and the released heat can be very high, depending on the source capacity. One of the key parameters in characterizing the jet fire is the radiative fraction. The previous study has correlated the radiative fraction to the source using a Froude number basis. Nevertheless, the flame mechanism and associated geometrical features gave significant effects on the global radiative heat flux to some extent. Therefore, the characterization of the main geometrical features, particularly on jet flame structures at higher momentum release conditions and its correlation with the radiative fraction, are valuable to be investigated. In this work, propane was used as fuel and released through a 9.8 mm circular nozzle with the exit velocities were set ranging between 27 and 65 m/s. It was found that the liftoff length estimation from this work is in a good agreement with the jet fire release under sub‐atmospheric pressure in a vertical orientation. Furthermore, the flame projected length and height were characterized by momentum‐driven length (L m) and buoyancy‐driven height (L b) by the dimensionless characteristics length (Ʌ). The experimental observations indicate that as the Ʌ ≥ 0.0001, the radiative fraction shows a decreasing trend.

Structure and Screech Tone of Radially Underexpanded Jet Emitted by Facing Cylinders

An underexpanded jet has typical shock-cell structure and strongly oscillates, its behavior being known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine, a pressure control valve and so on. When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially. Such underexpanded impinging jet is one of models of supersonic jets on laser cutting process and glass tempering process. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two cylinders, was experimentally examined for different nozzle pressure ratios and for different diameters of cylinder. Jet structure was analyzed by means of a visualization e.g. Schlieren method. A noise emitted from the jet was measured and the frequency of screech tone was analyzed. The experimental results were compared with those of a two dimensional jet issuing from a rectangular nozzle. Furthermore, a comparison of visualized sound waves with the screech tone frequency reveals that the sound source measured was in the vicinity of the end of the second cell and that the length of the second or third cell was one of the most important parameters to determine the frequency of the emitted screech tone.

Numerical Simulation on Hydraulic Characteristics of Nozzle in Waterjet Propulsion System

As an important over-current component of the waterjet propulsion system, the main function of a nozzle is to transform the mechanical energy of the propulsion pump into the kinetic energy of the water and eject the water flow to obtain thrust. In this study, the nozzle with different geometry and parameters was simulated based on computational fluid dynamics simulation and experiment. Numerical results show a good agreement with experimental results. The results show that the nozzle with a circular shape outlet shrinks evenly. Under the designed flow rate condition, the velocity uniformity of the circular nozzle is 0.26% and 0.34% higher than that of the elliptical nozzle and the rounded rectangle nozzle, respectively. The pump efficiency of the circular nozzle is 0.31% and 0.14% higher than that of the others. The pressure recovery and hydraulic loss of the circular nozzle are superior. The hydraulic characteristics of the propulsion pump and waterjet propulsion system are optimal when the nozzle area is 30% times the outlet area of the inlet duct. Thus, the shaft power, head, thrust, and system efficiency of the propulsion pump and waterjet propulsion system are maximized. The system efficiency curve decreases rapidly when the outlet area exceeds 30% times the outlet area of the inlet duct. The transition curve forms greatly affect thrust and system efficiency. The transition of the linear contraction shows improved uniformity, and the hydraulic loss is reduced. Furthermore, the hydraulic performance of the nozzle with a linear contraction transition is better than that of others.

Underexpanded Supersonic Jets from Elliptical Nozzle with Aft Deck

An experimental investigation of an underexpanded supersonic jet issuing from a circular nozzle, an elliptical nozzle, and an elliptical nozzle with an aft deck at different nozzle pressure ratios (NPRs) is reported in this paper. Static-pressure measurements over the nozzle walls were analyzed to understand the internal flow structure. Schlieren visualization and conical probe measurements were conducted to elucidate the development of the jets issuing from the nozzles. The sound-pressure level in the near field was measured, and it was found that the screech amplitudes were 26 dB lower in the elliptical nozzle with an aft deck. The screech-tone frequencies were observed to be above and near audible region (16 kHz) in the presence of the aft deck at NPRs 3 and 4. The jets emanating from the circular and truncated elliptical nozzles were observed to be flapping about the jet axis at NPRs 3 and 4. The unsteadiness of the jet was reduced by locking the jet onto the aft deck. The centerline Mach-number decay revealed that, due to the screeching effect, the truncated elliptical nozzle has a shorter potential core length and larger jet spreading. The flow separation and reattachment were observed over the aft-deck surface for higher NPR conditions.

Experimental and Numerical Investigations of Synthetic Jet Used for Electronic Cooling

Cooling of electronics and micro-electronics devices is an important task in our present world. Synthetic jet is a relatively new technique for electronic chip cooling which synthesizes stagnant air to form a jet resulted from periodic oscillations of a diaphragm in a cavity. Synthetic jet cooling increases the rate of heat transfer as compared to other cooling techniques. The impingement heat transfer characteristics of a synthetic jet is studying in this work. Synthetic jet is driven by a piston-cylinder arrangement a through circular nozzle for the impingement of jet on the heated surface. Air is considered as the cooling medium. Heat flux is taken as 8000W/m2. Numerical simulations and experimental methods are conducted to study the effect of various distance between the orifice and the heated plated(Z). A circular orifice is used to study the characteristics of convective heat transfer. The results are verified by the time history of convective heat transfer characteristic and validated with experimental results. The model was simulated to investigate the dispersion of heat flow on the walls using a mathematical turbulent model of k- ω SST. The Reynolds number (Re) is in the range of 4000-8000 based on average velocity, while the normalized impinging distance varies between 2D to 10 D The results shows the significant influence of Z/D ratio and sinusoidal wave frequencies to the heat transfer rate obtained. Experimental and numerical investigations is carried out to study the variation of Nusselt number with jet velocity. It is found that the Z/D ratio at 6 gives the maximum amount of cooling for a flat plate.

Mixing characteristics of inclined dense jets with different nozzle geometries

In the present study, we performed a laboratory investigation to examine the mixing characteristics of 45° inclined dense jets from different nozzle geometries using the technique of Planar Laser Induced Fluorescence (PLIF). The geometries included the circular, square and diamond shapes, as well as the duckbill shape of non-return duckbill valves that are now commonly used for brine outfalls and the star shape of non-return star valves that are available commercially but have not been adopted so far. The concentration centrelines, cross-sectional profiles and spread widths were quantified in the experiments. The results showed that the circular, square and diamond nozzle geometries have similar behavior, implying that the differences of their discharge length scale are not sufficiently large to induce a significant effect. On the other hand, the duckbill and star nozzle geometries have relatively higher dilutions both at the centreline peak and return points. Interestingly, the duckbill nozzle has a relatively lower rise height compared to the others, potentially due to the strong influence of axis-switching effect. In addition, we also performed numerical simulations using the Large Eddy Simulations (LES) approach with the Dynamic Smagorinsky sub-grid model for the diamond, duckbill and star shape nozzle geometries in the experiments. The comparison showed that the time-averaged geometrical characteristics from the three different nozzle geometries can be simulated reasonably well before the centreline peak but with slight over-predictions after that. Meanwhile, the dilution characteristics are underestimated by ~25% generally, which are similar to previous LES results with the reference circular nozzle. The spectral density distribution of the concentration fluctuations clearly demonstrated that the production of turbulence energy in the larger eddies is enhanced by the non-circular nozzles, which is also consistent with the increase in dilutions with these nozzles.

Effects of bevelled nozzles on standoff shocks in supersonic impinging jets

Abstract Moderately under-expanded jets issuing from a circular baseline and two bevelled circular nozzles impinging upon a perpendicular flat plate were experimentally studied. The effects of nozzle-pressure-ratio and separation distance variations on the standoff shock formations were investigated with schlieren visualizations and a visual hull based three-dimensional (3D) shock reconstruction technique to provide deeper insights into their 3D features. Across all flow configurations arising from the different combinations of these parameters, results indicated that the bevelled nozzles are effective in introducing asymmetry to the standoff shock geometries. Depending on the exact flow configuration, standoff shock locations may also undergo significant upstream displacements. In particular, the single-bevelled nozzle produces highly unsteady standoff shocks with asymmetric oscillation amplitudes along both side of the nozzle lip regions. Changes to the standoff shock key characteristics were observed to be sensitive towards the jet shock structures and reflection point modified by the bevelled nozzle exits. In particular, the strength and relative position of the reflection point are identified as the major contributing factors influencing the upstream static pressure distribution of the standoff shock, hence leading to the observed changes in the standoff shock behaviour.

Experimental Studies on Decay and Spread Characteristics of an Overexpanded Triangular Supersonic Jet

Experiments were conducted on overexpanded equilateral triangular supersonic jets (Mach 1.8) at Reynolds numbers 6.71 × 105 and 4.81 × 105 to study their decay and spread characteristics by means of measuring the jet centreline and lateral total pressure distributions. Schlieren images of the jets were also taken to study the shock patterns in the jet structure. The above Reynolds numbers correspond to the nozzle inlet total pressures of 550 kPa (6.71 × 105) and 360 kPa (4.81 × 105). For comparison purposes the above experiments were repeated on a circular nozzle with the same exit area and area ratio (1.44) and total pressures. The observations from the experiments reveal that the triangular jet exhibits a shorter supersonic core compared with the circular jet, i.e., reduction of 34.25% at 360 kPa and 31.11% at 550 kPa. The total pressure decay is more abrupt and a greater loss of the total pressure occurs closer to the nozzle exit plane in the case of the triangular jet compared to the circular jet. The lateral total pressure distribution reveals that the jet spreading rate is greater on the flat than on the corner side of the triangular jet.

The Development of Top-Hat Flow Field in a Circular Symmetrical Subsonic Nozzle

In this work, the numerical analysis and experimental measurements were made to investigate the development of top-hat flow field at atmospheric pressure in a circular symmetrical subsonic nozzle. Measurements were carried out over a range of inlet velocities (about 0.07-7 m/s) based on a nozzle with constant geometric parameters, which also provided verification for the numerical simulation. The objective of this study was to determine the change of top-hat flow field from the well-known pipe velocity profile to the saddle-back distribution as well as the key behaviours for the process. Results revealed a close coupling relationship between the process and the pressure gradient inside nozzle. It was concluded that the local flow direction of fluid near the edge of cross section was changed by static pressure gradient and overlapped with the mainstream. The increase in kinetic energy of each gas particle on the cross section was different contributed to the formation of top-hat flow field. The saddle-back distribution seems to occur after the appearance of the critical position. In addition, the influence of inlet velocity on the location of critical position as well as the degree of saddle-back distribution was also concerned.

Effects of Nozzle Geometry on Turbulent Characteristics and Structure of Surface Attaching Jets

The effects of nozzle exit geometry on the characteristics of a surface attaching jet were investigated experimentally. Three different types of nozzle geometries were studied, including a circular, square and rectangular nozzle with the same exit area. The jets were discharged with an offset height of two nozzle width at a Reynolds number of 5500. A particle image velocimetry system was used to measure the flow. Instantaneous visualizations revealed that the largest enhancements in the near field mixing and entrainment occur in the minor plane of the rectangular nozzle compared to the square and circular nozzles resulting in more rapid expansion of the shear layer. This also caused a faster deflection of the jet towards the free surface, maximum velocity decay and spread rates of the rectangular jet with minor axis orientation. The jet-surface interaction was examined using surface velocity, vorticity thickness and surface turbulence intensities. It was found that the damping of the surface-normal velocity fluctuations at the free surface is more severe in the minor plane of the rectangular jet than the square and circular nozzles. The influence of the free surface was also felt in the profiles of mean velocity and Reynolds stresses. The attenuation of Reynolds shear stress due to confinement was more dramatic in the minor plane of the rectangular nozzle than the other geometries. To quantify the influence of nozzle geometry on the coherent structures in the interaction region, two-point correlations of the velocity fluctuations and swirling strength; and proper orthogonal decomposition were performed.

Управление скоростью перемещения вязкоупругих материалов в цилиндрическом канале шнекового питателя формующих устройств

The present research features the problems of wheat processing. Wheat processing has its own specific features. For instance, the process of gluten extrusion forming is very complex since it is associated with the visco-elastic and adhesive properties of raw gluten. The article discusses the results of applying the numerical finite difference method to the Navier-Stokes equation in the case of the one-dimensional problem when a cooled viscoelastic material has to pass through circular nozzles. The paper also features the obtained surface model of velocity evolution and some averaged results for the possible automation of the process. The viscosity properties of raw gluten are variable and depend on temperature, chemical composition, and properties of the raw material. Modeling makes it possible to characterize the properties of the material and its behavior in various situations. Such research demands neither additional time nor significant costs. The authors identified patterns of movement for raw gluten in the extrusion molding unit and selected the most appropriate automation system to control the speed of its movement to the molding assembly in the grinder feed screw. The significance of the research is obvious for subsequent physical and mathematical modeling of heat and mass transfer processes of vacuum freezing and drying and granulating of gluten extrusions. The results of the research presented in the article are consistent with the available information on this topic. The present approach to solving the problem of choosing the best rational hydrodynamic regimes was applied due to the complexity of the experimental determination of velocity fields and the difficulty of analyzing the Navier-Stokes system of hydrodynamic differential equations with variable proportionality coefficients.

Flame profile parameters of horizontal turbulent jets: Experiments, similarity analysis and an integral model

The present study provides a comprehensive model for flame profile parameters of horizontal turbulent jets, including the flame horizontal projection distance, the flame vertical height, the flame trajectory and the flame cross section radius, which have not been completely quantified previously. Experiments are carried out with circular nozzles (diameter: 3, 4, 5, 6 mm) employing propane as fuel with a wide range of discharge velocity, which covers both buoyancy- and momentum-controlled jet conditions. Similarity analysis of the fluid dynamics is developed to determine the flame horizontal projection distance and flame vertical height in terms of the initial jet momentum and an effective buoyancy of the flame, which together determine a characteristic length scale and a characteristic volumetric flow rate for interpreting the data. Moreover, an integral model based on top hat similarity of the flow profiles is derived to support the non-dimensional analysis, and in addition to predict the flame trajectory and flame cross section radius. The integral model includes equations for air entrainment and for momentum conservation of the flow, where both the normalized flame horizontal projection distance and the normalized flame vertical height show asymptotic behaviors consistent with small initial momentum condition and large initial momentum condition, respectively. The proportionality constants of the top hat similarity profiles are determined based on the developed theory and the experimental data, from which also an effective entrainment coefficient is derived and the flame cross section radius is resolved. The present study provides new similarity analysis and a comprehensive model for the flame profiles of horizontal turbulent jets.

Parametric Design Method and Performance Analysis of Double S-Shaped Nozzles

A parametric design method, which was based on super-elliptical transition and self-adaption infrared radiation shield for the double S-shaped nozzle, was introduced. The complete shielding of high-temperature components in the S-shaped nozzle was realized. Model experiments and numerical simulations were performed to investigate the effects of offset ratioS/D, the ratio of length to diameterL/D, and the aspect ratioW/Hon the aerodynamics and infrared radiation. The results showed that the total pressure recovery and thrust coefficients were improved initially, but dropped rapidly with the increase in offset ratios with the range of investigated parameters. There existed an optimal offset ratio for the aerodynamic performances. Considering the weight penalty, the length of nozzles should only be increased properly to achieve better aerodynamic performances. Both friction and viscous losses caused by large streamwise vortices dominated the aerodynamic performances of nozzles. The nozzle with the aspect ratio ofW/H=5.0was recommended for achieving optimal aerodynamics. The increase in aspect and offset ratios could effectively suppress plume radiation, which was, however, not sensitive to overall radiation. Compared to circular nozzles, double S-shaped nozzles reduced overall infrared radiation by over 50%, which proves significant stealth ability. A balance between aerodynamic performances and infrared radiation suppression could be reached for double S-shaped nozzles.

ЧИСЛЕННЫЙ РАСЧЕТ ПОЛЕЙ СКОРОСТЕЙ УПРУГО-ВЯЗКИХ МАТЕРИАЛОВ В ЦИЛИНДРИЧЕСКОМ КАНАЛЕ

The article touches upon the application of the numerical finite difference method for solving Navier-Stokes equation in case of one-dimensional problem of passing a cooled viscoelastic material inside circular nozzles. There have been analyzed the specific features of using the method and presented the results of its application. The object of study was not chosen at random, because viscous properties of raw gluten are variable and depend on the temperature, chemical composition and properties of the feedstock. Working not properly with the object of research (phenomenon, process), but with its model helps to characterize its properties and behavior in various situations relatively quickly and without significant costs. The need to identify patterns of internal heat and mass transfer, which is based on studying the kinetics of the process, is obvious for physic-mathematical modeling of heat and mass transfer processes of wheat gluten granulation, in particular, analyzing the mechanism of moisture removal during its drying under radiation power supply. The results of the conducted research are consistent with the available data on the subject, and the suggested approach to solving the problem of choosing rational hydrodynamic regimes has been applied due to the difficulty of experimental determining the velocity fields and problematic analyzing the system of hydrodynamic differential Navier-Stokes equations with variable proportionality ratios.